The principal objective is to characterize physical and chemical events intermediate between the absorption of energy and the expression of radiation-induced damage in cells. Two principle test objects are 1) the inert bacterial spore and 2) the molecular transforming principle. With these, standard chemical free radical techniques can be used to measure radiation chemical change to be correlated with biological effect. The aim is to correlate the two. A variety of modifiers of radiation injury will be used. Organic sensitizers, especially p-nitroacetophenone whose mechanisms of action have been partly revealed in this laboratory, and a series of inorganic sensitizers, especially metal ions and metal complexes, will be studied. Our work has demonstrated the participation of the hydroxyl radical in many of these sensitizing actions, and allows that some sensitization in some instances does not involve hydroxyl radical. These studies in the past have been done with bacterial spores. These experiments will continue covering a large number of metals with different redox properties. Study of molecular DNA will include the transforming DNA of B. subtilis to be irradiated in vitro in the manner revealing the action of hydroxyl radicals in spores. In addition to physico-chemical measurements of damage, tests for retention of transforming ability will be routine. Emphasis will be given to the taking up of sensitizing agents by cells to correlate, directly, concentration with activity. Application of the general techniques in free radical investigations developed for cells in this laboratory will be made to radiation-induced mutagenesis in the spore. These studies are significant for mechanisms of sensitization of anoxic tumor cells in vivo for establishment of rationales for development of sensitizing compounds. Also significant is the fact that metal ions are good radiation sensitizing agents, because of the increases in environmental metal and radiation levels. In this connection the role of these substances in increasing mutation rates and the chemical mechanisms by which these are accomplished are of grave significance.